The present invention relates to a semiconductor laser device for projecting a laser beam from a semiconductor laser to an end surface of a solid-state laser medium and for irradiating a high-output laser beam by optical pumping (photo-excitation).
An LD solid-state excitation laser is known, which uses a semiconductor laser as an excitation light source or a light emitting source of an excitation light, and which amplifies and projects a laser beam from the light emitting source.
Referring to FIG. 19, brief description will be given below on an LD solid-state excitation laser.
In FIG. 19, reference numeral 1 denotes a light emitter, and 2 denotes an optical resonator. The light emitter 1 comprises an LD light emitting source (semiconductor laser element) 3 for emitting a laser beam as an excitation light, and a condenser lens 4. Further, the optical resonator 2 comprises a laser crystal (Nd:YVO4) plate 6 where a reflection mirror 5 with a dielectric reflection film is formed, and a transparent output reflection plate 8 having an output mirror 7 with a dielectric reflection film on it. At the optical resonator 2, the laser beam is pumped, resonated and amplified, and the laser beam is then outputted.
The laser crystal plate 6 is a solid-state laser medium for performing amplification of light. The solid-state laser medium is, for instance, a solid-state crystal plate using Nd ions or Yb ions as laser active ions. As the laser crystal plate 6, YAG (yttrium aluminum garnet), etc. doped with Nd3+ ions is adopted, for instance.
YAG has oscillation lines of 946 nm, 1064 nm, 1319 nm, etc. The laser crystal plate 6 is not limited to YAG. Nd:YVO4 with oscillation line of 1064 nm, Ti:Sapphire with oscillation lines of 700 nm to 900 nm, or a dye laser material with laser dye dispersed in transparent solid material (such as glass, PMMA (macromolecular material)) may be used.
As the light emitting source of the excitation light, the semiconductor laser element (semiconductor laser diode (LD)) is widely propagated as a material for emitting a high-output laser beam at low electric power. Further, there have been strong demands on the laser beam of higher output in recent years. To meet such demands, attempts are now being made to provide the laser beam with higher output by using a plurality of semiconductor laser elements and by bundling together the laser beams emitted from the respective semiconductor laser elements.
One of the methods to bundle the laser beams together is a method to use optical fibers 11 as shown in FIG. 20. Laser beams emitted from the respective semiconductor laser diodes 3 are projected to the optical fibers 11 independently from each other. The optical fibers are then bundled together, and a laser beam is emitted from the bundled optical fibers as an excitation light.
As disclosed in the Japanese Patent Publication 7-112083 of examined patent application, a multiple of laser beams emitted from a multiple of semiconductor lasers are turned independently to parallel beams by a lens array. Further, by a second lens, the laser beams are converged to an end surface of a solid-state laser medium.
In a conventional type semiconductor laser device of high output type as described above, which uses a plurality of semiconductor laser elements, laser beams from the semiconductor laser elements are bundled together by optical fibers. This makes an optical system more complicated. Or, a lens with a large diameter is required because a multiple of laser beams are converged by a lens array. Binding loss due to the binding of laser beams is high, and this leads to the problems such as heating or thermal deformation of optical components caused by the loss of light. Further, when the laser beams are bundled together, excitation input to the solid-state laser medium is increased. In some cases, such problems may occur that the solid-state laser medium may be cracked or thermal distortion may occur. Or, it is difficult to maintain laser characteristics of the projected laser beams.